Light metal piston with reinforcement and the like



May 28, 1957 M. e. WHITFIELD LIGHT METAL PISTON WITH REINFORCEMENT, ANDTHE LIKE Filed May 7, 1953 INVENTOR.

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United tates Patent masses LIGHT METAL PISTON WlTi-H REINFORCEMENT ANDTHE LliKE Marshall a. Whitfield, Garden-City, N. Y.

Application May 7, W53, {aerial No. 353,5llll l1 Qiaims. (Cl. do -14}Pistons for internal combustion engines have long been madeadvantageously from light metal such as aluminum and its alloys. Suchpistons are normally grooved for the acceptance of piston rings whichoperate to seal the pistons against the walls of the cylinders in whichthey operate. It has also been realized that the piston rings tend toenlarge the grooves in which they are located by wear, the wear beingespecially rapid in the light metals used for the formation of thepistons. As a consequence, much work has been done in the field of theformation of composite pistons having a light metal body and variousforms of inserts of harder metal, moreresistant to wear. A common formof such inserts is an annulus or ring of cast iron which was caused toform that part of the piston structure in which the piston ring groovesare machined. The composite struc ture could bemade in various ways asby locating an iron or steel annulus in a mold suitable for casting apiston and then introducing the molten light metal into the mold in sucha way as to cast a piston body in which the annulus was embedded in aproper position. Again a light metal piston body could be formedseparately as by casting or forging, an iron or steel annulus could beassembled-to the body, and with both parts located in a suitable mold,molten light metal could be cast between the annulus and the pistonbody.

The formation of light metal pistons with hard metal inserts involves anumber of problems. For one thing the inserts are themselves a matter ofsome expense. For another they addsignificantly to the total weight ofthe piston. In the third place insertssuch as cast iron are under somecircumstances subject to breakage. In

the fourth place it has been found exceedingly difiicult to produce sucha bond between the light metal of the piston body and the harder metalof the insert as will maintain integrity of the structure underconditions of use. It will be understood that continuous annular insertswhich are grooved to accept the piston rings not onlyare subjected tosevere mechanical strains which tend to separate them from thepistonbodies, but also that under conditions of substantial differencesin rates of thermal expansion, severe forces are set up tending todisrupt any bond which may be formed.

The primary object of my invention is me provision of astructure andmethod of making it in whieh the problems set forth above are solved orameliorated, while the wear advantages of previous structures are retained. More specifica-lly it is an object of my invent-ion to. provideareinforced piston in which differences in thermal expansion do notten-cl to free the inserts from the'body of' the piston. It is an objectof my invention toprovide a reinforced piston which is lighter, lessexpensive to make and safer to use because insertion elements cannotbe'freed from the piston body to damage the piston or the cylinderwalls.

These and other objects of my invention which will be set forthhereinafter or will be apparent to one skilled ice in the art uponreading these specifications I accomplish by that construction andarrangement of parts of which I shall now describe certain exemplaryembodiments. Reference is made to the accompanying drawings herein:

Figure 1 is an elevational view of apart of a reinforcing element whichI may employ.

Figure 2 is a view of the upper portion of a piston made in accordancewith my invention, a part of the view being in elevation and a part insection.

Figure 3 is partially a sectional and partially an elevational view of apiston taken along the line 3-3 of Figure 2.

Figure 4 is an enlarged, partially sectional view taken along thesection line 4-4 of Figure 3.

Figure 5 is a similar enlarged sectional view showing the use ofanotherform of the reinforcing element.

Figure 6 is a partial plan view of the reinforcing element usedinforming the structure of Figure 5.

Figure 7 is an enlarged, partially sectional view similar to that ofFigures 4 and 5, but showing yet another form of reinforcing structure.

Figure 8 is a combined side and end elevational view of the type ofreinforcement employed in the structure of Figure 7.

Figure 9 is a transverse sectional view of a mold structureillustratinga method of positioning my reinforcement structures prior tocasting.

Figure 10 is a partial plan View of yet another type of sinuous metalreinforcement.

Figure 11 shows in perspective a reinforcement of expanded sinuositymaking for elongated, though comparatively' widely interspaced, areas ofreinforcement in the grooves.

Figure 12 is a similar view of a reinforced structure wherein the areasof reinforcement, while elongated, are less widely spaced.

Brieflyin the practice of my invention I employ for reinforcementpurposes one'or a series of elements formed from wire, rod or'othersimilar stock configured to have sinuosity at least in the direction ofthe general extent of the element. The reinforcing elementscharacterized by the sinuosity just referred to will be configured so asto conform to the curvature of the periphery of a piston.

r At the ends of the elements, the wire or rod stock may be bentoutwardly or inwardly to provide projections 'by means of which theelements may be definitley and posi tively located in the moldas'hereinafter explained. The reinforcing elements maybe employed withlight metal piston bodies preformed by casting or forging in anoperation in whichilight metal is cast into the mold to join thepreformed structure. with the reinforcing'element or elements. Again,andxmore usually, the reinforcing element or elements will be located inthe mold, and the light metal body formed completeiin the same mold bycasting. In either event, in accordance with the practice of my in=vention in its preferred form, the reinforcing element or elements willbe entirely embedded in the portion of the structure formed by theintroduction of molten metal into the mold. By the term entirelyembeddedfl mean to indicate a preferred condition in which thereinforcing element'or elements will be encased within the cast metalafter such finishingoperations as may be applied to the piston prior touse; such as turning, grinding, and the like.

It will be understood that any projecting ends of the reinforcementelementor elements will be removed as a part of such finishingoperations. Furthermore, in .accordance with my invention a piston ringretaining groove or grooves'will be machined in the piston structure insuch a way as to cut across the embedded reinforcement, as will behereinafter m'ore fully'explained.

To illustrate one form of the invention, reference is made to Figure 1wherein I have illustrated a portion of a structure formed of wire 1bent in a sinuous fashion to present oppositely directed loops 2 and 5with straight portions of the wire between them as at 6. This is oneconvenient form of sinuous structure which can readily be made on a wirebending machine. In the form shown in Figure 1 the sinuosities lie in asingle plane and the structure may be formed continuously in suchlengths as may be desired for convenient handling. The exemplarystructure is formed of drawn steel wire of circular crosssection; but itmight be formed of rod stock, of extruded or drawn shapes which are notcircular in cross section, or even of narrow strips cut, as by slitting,from sheet or strip stock. An additional advantage of using reinforcingstructures made of drawn or rolled products lies in the toughness of themetals as distinguished from the brittleness which is frequently acharacteristic of cast structures. The thickness or diameter of the wireor other element used to form the structure of Figure 1 may be widelyvaried and may be determined by such factors as cost and weight.Normally it will be determined also, at least as to a maximum, by thethickness of the piston walls at the place where the reinforcement is tobe used, since the preferred practice of my invention the reinforcementis to be entirely embedded in the cast metal as explained. The nature ofthe convolutions or sinuosities formed by the wire or the rod in thestructure may be considerably varied. I prefer that the straight partsor legs 6 of the structure (or any portions connecting the loops 2 and5, irrespective of their shape) be spaced from each other by a distanceat least as great as the diameter or thickness of the wire or rod andpreferably from two to about five times the diameter. This also is forthe purpose of permitting the positive embedding of the reinforcementwithin the cast metal under circumstances where it is necessary for thecast metal to flow through the sinuous structure.

The transverse distance between the loops 2 and 5 at opposite sides ofthe sinuous structure may be varied as desired. The sinuous structurewill be embedded in the wall of a piston and normally at least onepiston ring groove will be machined or ground into the piston wall insuch a way as to cut across the reinforcement. If a given reinforcementis to be cut by only one groove the loops 2 and 5 may be close togetherand the intermediate parts 6 very short. If, however, two or moregrooves are to be. cut with respect to any one reinforcing structure,then the loops 2 and 5 will be separated by a suitable distance for thepurpose, the intermediate parts 6 being relatively long.

Having formed a structure such as that shown in Figure 1, where it is tobe embedded in the circular side wall of a piston, I next curve thestructure to a radius conforming to the curvature of the piston wall andcut it to a desired length. In doing this, provision is made forprojecting end portions of the wire or rod at the extremities of areinforcing element. These may be bent outwardly at the time of theformation of a reinforcing element from a continuous length of thestructure shown in Figure 1. Again the wire bending machine used to formthe structure of Figure 1 may be so operated as to form sinuousstructures of a predetermined length with extending portions initiallyformed at their ends.

The nature of an exemplary finished form of the reinforcement elementwill be appreciated from Figure 9. Here I have shown a mold (for apiston) in section as comprising opposed parts 7 and 8 which, beingbrought together, define a mold cavity 9 in which molten metal may bepoured or cast. Within the mold I have shown a sinuous reinforcingelement at 10. This sinuous element is so shaped as to follow thecontour of the mold wall in the part 7. At the ends of the reinforcingelement 10 I have shown projecting portions of the wire at 11 and 12.These pass through appropriate orifices in the mold at the meeting linesof the mold parts .7 and 8 and serve to support the reinforcing element10 within the mold in its proper position. The preferred position is onein which the reinforcing element 10 follows the contour of the walls ofthe mold part 7 but is supported out of contact with them so that themolten casting metal in filling the mold can lie between the reinforcingelement 10 and the mold walls, whereby entirely to embed the reinforcingelement.

In Figure 9 I have also shown located within the mold a similaroppositely disposed reinforcing element 13 having projecting portions 14and 15 at its ends whereby it is supported in the mold cavity. A pistoncast within the mold illustrated in Figure 9 will have a band or zone ofreinforcement extending throughout its circumference, as will beunderstood from the figure. I shall hereinafter refer to this ascontinuous circumferential reinforcement without implying, however, thatthe reinforcing element itself is continuous circumferentially. Tworeinforcing elements have been used to make up the continuouscircumferential reinforcement in Figure 9, and more could be used ifdesired. Under some circumstances less than full circumferentialreinforcement may be found preferable. The wear in pistons is primarilyat opposite ends of a line drawn perpendicular to the axis of the wristpin by which the piston is pivoted to the so-called connecting rod. As aconsequence, in many pistons it may be found sufficient to reinforceonly about degrees of arc of the piston circumference at each side ofthe piston, i. e., 60 degrees of are at each side of each end of theaforesaid line perpendicular to the axis of the wrist pin. Suchrelatively short sections of reinforcement may be supported byprojecting wire ends such as those hereinabove described, passingthrough appropriate perforations in the mold parts. It may be pointedout that bosses for accepting the wrist pins are illustrated in Figures2 and 3 at 16.

When the light metal is cast in the mold it will wholly embed thereinforcement or reinforcements excepting for the projecting endsthereof which in the finishing operation will be cut away. The embeddedcondition of the reinforcement will be evident in Figures 2, 3 and 4,the piston as a whole in these figures being indicated by the numeral17. It will be usual in the finishing of the piston for use to mill oneor a plurality of piston ring grooves. Two of these grooves have beenindicated at 18 and 19 in Figures 2 and 4. In this instance both grooveshave been milled or turned in the piston body across the area occupiedby the reinforcement. The result is that the loop elements 2 of thereinforcement lie above the groove 18 while the loop elements 5 of thesame reinforcement lie below the groove 19. Between the grooves aportion of the straight-away parts of the reinforcement remains as at611 in Figure 4. It will be evident that the opposed side edges of thegrooves are reinforced and faced in part by cut end portions of thereinforcing structure, which being harder and more durable than thelight metal cast around them, impart added durability to the grooves anddiminish wear, thus serving the general purpose of reinforcementsheretofore used, but without many of their disadvantages.

With reinforcements of the wholly embedded type herein taught, thematter of bond between the reinforcement, and the light metal castaround it becomes of relatively much less importance. Various expedientsmay be adopted to secure bond if desired. Thus, the wire used to form myreinforcement may be iron or steel wire which has been continuouslycoated with aluminum by hot dipping. When this is done, a bond canreadily be formed between the hot dipped coating already on the wire andthe aluminum or aluminum alloy cast against the wire. Even better bondscan, in many instances, be secured by first coating the iron or steelwire with a thin layer of a metal such as tin, zinc or nickel. Sinceonly very thin applications of such metals are necessary, they areconveniently applied by electroplating, although in the case of zinc,hot dipping may be practiced: In casting the light metal against thereinforcement I may, with advantage, practice teachings setfforth in mycopending application, Serial No. 309,773, filed September 16, 1952 andentitled Casting LightMeta-l'Against Iron, and Article Formed Thereby.The use of'a casting procedure in which the molten cast metal is causedto flow against the surfaces of the reinforcement for a substantiallength of time is of advantage in eliminatingthe effect of oxides whichmay be found either on the surface of the treated wire or on thesurface'of the molten light metal as it contacts the wire; and where thelight metal is an alloy high in elements such as silicon, such forexample as vanasil, the temperature conditions may beso arranged thatthe reinforcement has a chilling effect on immediate adjacent portionsof the molten metal, resulting in a precipitation of some of the siliconor other alloying ingredient in a very finely divided form withconsequent improvement of the bond.

As indicated the matteref bond is of relatively less importance in mystructuresdue-tothe form of the reinforcement. It will be understoodfrom Figure 4 that the reinforcement portions 2 and are of loop shape sothat they cannot be dislodged even if the bond is poor, because of theirwholly embedded condition. The portions'fia ofthereinforcementillustrated in Figure 4 are the only portions whichwould besubjeet to any movement in' the event of bond failure.These'portions may be so shaped, if desired, as to prevent axialdisplacement. One way of doing this is to subjectthe reinforcementelements, such as shown in Figure '1, to dies or rollers so shaped as toimpart a kink or bend to the portions 6 connecting the loops 2 and 5.This is illustrated in Figure 6, the bends being illustrated at 20.Figure 5 shows such a reinforcement embedded in a piston 17a. The loopmembers 2 and 5 are as before; but the bend in the intermediate portions6b is such as to prevent axial displacement.

It has been stated that the thickness of the wire or other stock used toform my reinforcements may be considerably varied depending upon theextent of reinforcement desired, and upon the thickness of the pistonwalls in the reinforced portion. Thus, it is possible to formreinforcing elements having such thickness or location that the millingor turning of the piston ring grooves does not cut entirely throughthem, in which event also the reinforcing elements will not be liable todisplacement upon bond failure.

While I have shown a reinforcing element cut by two piston ring grooves,it will be understood that the reinforcement may be so shaped andproportioned that a greater number of grooves may be formed across it,or that the reinforcement may be so shaped and proportioned as to acceptonly one groove. In the latter event, if more grooves are desired inreinforced condition, a plurality of reinforcements may be employedlengthwise of the piston.

My reinforcements may take other forms than those hereinabove described.By way of illustration, I have shown in Figure 8 a reinforcement 21which is formed of wire in the shape of a flattened spring. Such areinforcement is shown wholly embedded in a light metal piston 17b inFigure 7. In this instance, in the formation of the piston ring grooves18 and 19, the spring-like reinforcement may cut through at one sideonly.

In Figure I have shown a type of reinforcement which may be made ofsheet metal or strip by a stamping or cutting operation. Thereinforcement is indicated at 22 and is characterized by alternatelyextending slits 23 and 24 which give sinuosity to the structure. Theslits should be of sufficient width to permit ready flow of the metalbetween them.

In Figure 11 a piston 25 is shown as provided with reinforcing elements26 and 27 of expanded sinuosity. Here where a piston ring 28 is formedin the cast body so as to intersect the crests of the sinuousreinforcements,

relatively'longer areas ofreinforcement will be formed, as will beevident from the figure, although these areas of reinforcement will becomparatively widely spaced.

Another shape of reinforcement is illustrated in Figure 12 where thepiston 29 has reinforcements 30 and 31. It is characteristic of thisform of reinforcing structure that'the wire or similar elements areprovided with alternately wide loops 32 and narrow loops 33. If the wideloops are located in such fashion that they can be intersected by thegroove 34, elongated areas of reinforcement will be formed but thesewill be comparatively closely spaced. Itis, of'course, characteristic ofthe types of reinforcement shown in Figures 11 and 12 that they must beaccurately located in the mold and positioned with respect to the'placeswhere'the grooves will be formed in order to serve their purpose to thebest effect.

My reinforcements as cast into the piston body are sinuous in adirection circumferentially thereof, and may be sinuous also (as showninFigure 7) in a direction radial of the piston. In either event, itwillbe seen that even where the material of the reinforcement has athermal coefficient of expansion widely different from that of thesurrounding light metal, this condition is not likely to result in bondfailure or separation of parts.

Modifications may be made in my invention without depart-ing from thespirit of it. Having thus described my invention in certain exemplaryembodiments, what I claim as new and desir-to secure by Letters Patentis:

1. A light metal piston havinga heavy metal reinforcement embeddedtherein, said reinforcement comprising a sinuous wirelike elementextending. in the direction of th'e'c ircurrife'rence of the said pistonand characterized by upwardly and downwardly extending bights.

2. A light metal piston having a heavy metal reinforcement embeddedtherein, said reinforcement comprising a sinuous wire-like elementextending in the direction of the circumference of said piston andcharacterized by upwardly and downwardly extending bights, and acircumferential groove extending inwardly from the cylindrical surfaceof said piston, said groove cutting the said wire-like elementintermediate its upwardly and downwardly extending bights.

3. A light metal piston having a heavy metal reinforcement embeddedtherein, said reinforcement comprising a sinuous wire-like elementextending in the direction of the circumference of said piston andcharacterized by upwardly :and downwardly extending bights, saidwire-like element being additionally characterized by sinuousity indirections radial of said piston.

4. A light metal piston having a heavy metal reinforcement embeddedtherein, said reinforcement comprising a sinuous wire-like elementextending in the direction of the circumference of said piston andcharacterized by upwardly and downwardly extending bights, a pluralityof circumferential grooves extending inwardly from the cylindricalsurface of said piston, said grooves cutting the said wire-like elementintermediate its upwardly and downwardly extending bights, there being aland between adjacent grooves, said wire-like element providing heavymetal loops on the outer sides of the outermost grooves and intermediateportions passing through the said land.

5. A light metal piston having a heavy metal reinforcement embeddedtherein, said reinforcement comprising a sinuous wire-like elementextending in the direction of the circumference of said piston andcharacterized by upwardly and downwardly extending bights, a pluralityof circumferential grooves extending inwardly from the cylindricalsurface of said piston, said grooves cutting the said wire-like elementintermediate its upwardly and downwardly extending bights, there being aland between adjacent grooves, said wire-like element providing heavymetal loops on the outer sides of the outermost grooves and intermediateportions passing through said land, the said intermediate portions beingcharacterized by a bend preventing lateral displacement thereof.

6. A light metal piston having a heavy metal reinforcement embeddedtherein, said reinforcement being formed of drawn Wire extending in thedirection of the circumference of said piston and characterized bycontinuous sinuousities in the said circumferential direction whollyembedded in said piston.

7. A light metal piston having a heavy metal reinforcement embeddedtherein, said reinforcement being formed of drawn wire coated with ametal coating acting to promote adhesion between the light metal and theheavy metal wire and extending in the direction of the circumference ofsaid piston and characterized by continuous sinuousities in the saidcircumferential direction wholly embedded in said piston.

8. A light metal piston formed of a material chosen from a classconsisting of aluminum and its alloys, said piston having a whollyembedded reinforcement extending peripherally therein, saidreinforcement consisting of ferrous wire and characterized by sinuosityat least in the peripheral direction.

9. A process of forming a reinforced light metal piston, which comprisesthe steps of forming a piece of Wirelike material into a curved sinuousreinforcement characterized by upwardly and downwardly extending bightsand outwardly projecting end portions, providing a mold,

supporting said reinforcement in said mold solely by means of saidprojecting end portions in such fashion that the sinuous reinforcementis held out of contact with the wall of said mold, casting light metalin said mold in such fashion as wholly to embed said reinforcementexcepting for the projecting ends thereof, and cutting a circumferentialgroove in said piston so placed as to sever upwardly and downwardlyextending legs of said reinforcement between said bights.

10. The process claimed in claim 9 wherein said wirelike material isformed of ferrous drawn wire, and wherein being wholly embedded in thebody of said piston.

References Cited in the file of this patent UNITED STATES PATENTS I2,685,729 Daub Aug. 10, 1954 FOREIGN PATENTS 455,539 France Dec. 13,1913 897,373 France Mar. 20, 1945 540,990 Great Britain Nov. 7, 1941548,400 Great Britain Oct. 8, 1942 642,042 Great Britain Aug. 23, 1950OTHER REFERENCES Automotive Industries, vol. 105, issue #9, Nov. 1,1951, Inside back cover.

